New pumps to fix Mosgiel's flooding woes

Mosgiel resident Shaun Bungard piles sandbags high in front of his Gordon Rd home during flooding earlier this year. Photo: ODT

Mosgiel is about to get two new pumping stations that should fix a situation in which wastewater backed up and overflowed from toilets and showers during the July floods.

The Dunedin City Council says pumping stations in Carlyle Rd and Reid Ave did not handle the rainfall, so stormwater entered the wastewater network instead of draining into the river.

To deal with the problem, the council has decided to replace both pumps.

During the flood, more than 120mm of rain fell in Mosgiel over a 24-hour period.

Council three waters group manager Tom Dyer said staff had spent a lot of time since the flood talking to residents and investigating the network to get a clearer picture of what caused the flooding.

''In most cases, flooding occurred because the network could not cope with the volume of water that fell.

''The new pumping stations will be designed to ensure that larger volumes of stormwater can be moved through the network efficiently.''

At a recent infrastructure services and networks committee meeting, Mr Dyer said during the flood some homes were subject to stormwater flooding and others to ''wastewater reflux''.

That meant wastewater backing up and coming back out of toilets and showers.

Mr Dyer described that as ''a really, really unfortunate set of events''.

The council concluded there was a clear link between the point the Reid Ave pumping station was overwhelmed and the effects on the wastewater system and on downstream properties.

Parts of Mosgiel were hit by 400mm of surface water, meaning a significant amount of water entered the wastewater system.

The proposed work would have benefits for both the stormwater and wastewater systems by reducing infiltration.

Mr Dyer said yesterday the pumping stations lifted a significant proportion of Mosgiel's water out of the stormwater drainage network and into the Silverstream.

When the water level rose above 200mm, gully traps where people's drains discharged into the sewer network got covered in water, and that water found its way into the wastewater network.

The cost of the work was not yet known, but he was ''pretty confident'' the improvements could be done within existing budgets.

In addition, monitoring of wastewater pipes in Tyne St and Carlyle Rd would continue, something that would help with planning for pipe network renewals .

Mr Dyer said the replacement of the pumping stations and other work was a ''significant start to improvements to Mosgiel's stormwater and wastewater network.''

david.loughrey@odt.co.nz